Horn capacitor

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Kentf1003

Senior Member
Repairing a 40-47 style Ford pickup horn and need the value and working voltage of the capacitor for replacement purposes. I figure that "Only the Shadow" Barners will know. Thanks.
 

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Found an answer on another site. Most recommended .5 at 250v. Some said it could go as high as 1mfd. For what it's worth.
 
I assembled the inside of the horn with a new .1 / 400v cap. Hooked to a 6V battery and ... nothing. Then tried closing the point gap. Suddenly, in the still of a Sunday morning, the loud blast awakened the neighborhood (and probably "The Shadow"). Lights came on, dogs barked, and I knew that all was well.
 
Kentf1003 said:
I assembled the inside of the horn with a new .1 / 400v cap. Hooked to a 6V battery and ... nothing. Then tried closing the point gap. Suddenly, in the still of a Sunday morning, the loud blast awakened the neighborhood (and probably "The Shadow"). Lights came on, dogs barked, and I knew that all was well.
Click to expand...

Did you hit your head on the hood? Because when that happens, you're supposed to hit your head.
 
any idea why the horn has a capacitor? after a little homework, I found that it buffers the points like in the distributor.
are the points normally closed?
thanks.
 
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Some examples help you any? These are 1935, 1936 and 1940 (not in the order of the photos, the round dashed drawing is 35, the one with the resistor is 40).
 

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thanks JSeery. the 1936 example does show the cap in series with the coil. which made no sense until I closed the points. and got the horn to work. so I think I answered my new second question about the points having to be closed. but maybe you can confirm that for me.
 
All three show the cap in parallel to the points and in series to the coil! Where are you seeing a difference? All of the diagrams are the same except for the addition of a resistor in the 1940.
 
bad wording on my part. I said "1936 example" only because I have a 1936 horn.
but all 3 pics show the points open. I can only get the '36 horn to work by setting the points closed. maybe the points are set open in the '40 horn? with the points open, DC current will flow thru the resistor but not the capacitor.
 
Points should be closed without voltage. The capacitor is there to absorb voltage spikes that would appear at the points as arcing, without it, increasing point life. The capacitor is in parallel with the points. Some of the aftermarket parts houses used to sell the diaphragm. If you have two horns they are not the same tone. The diaphragm's are slightly different (Thicker). You may want to increase the capacitor voltage rating to 600V
 
fenbach said:
bad wording on my part. I said "1936 example" only because I have a 1936 horn.
but all 3 pics show the points open. I can only get the '36 horn to work by setting the points closed. maybe the points are set open in the '40 horn? with the points open, DC current will flow thru the resistor but not the capacitor.
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Ok, sorry I didn't follow what you were saying! Believe the points would have to be closed in order for the current to flow when first activated, you are correct.
 
The horn ******** coil sometimes need a good kick to get the oscillation going. The 6-volt systems needed all the help they can get. Once it's working, the cap doesn't get much time to build another full charge like it does in an ignition system plus there is no inductor in the circuit like an ignition system. The later cars did away with the capacitors but they were still used by some manufacturers till the 12-volt systems prevailed.
 
You need the same amount of power to make a horn sound so loud.
With only 6v availabe you have a higher current passing through the points.
The higher current is hard on the points and therefor you need the cap to make them last longer.
With 12v you have half the current and points will last longer.
The horn coil will also release a a voltage spike when the magnet field is changing.
The cap is not charged up to help the horn, while resting its shorted out by the points and empty.
 
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